The present invention generally relates to a method and apparatus for plate winding of a long sheet to be used in a winding operation of a long film around a plate bobbin in the manufacturing of, for example, a laminated film capacitor.
A conventional method of winding a long film around a plate bobbin will be described hereinafter with reference to FIG. 22 through FIG. 26. A method of rotating a conventional plate bobbin 32 in the winding of a film 31 around the plate bobbin 32 is shown in FIG. 22. The plate bobbin 32 rotates in a direction of an arrow mark. Its rotary shaft 32a is in a home position and does not move. The film 31 advances in a direction of the arrow mark and is wound around the plate bobbin 32 through an expander roll 36.
FIG. 23 and FIG. 24 are side views showing the conventional plate winding method. The film 31 is wound around the plate bobbin 32 through pass rolls 33, 33a and 33b, a free dancer roll 34, a forced dancer roll 35 and the expander roll 36. The plate bobbin 32 rotates in the direction of an arrow mark, but its rotary shaft 32a is in a home position and does not move.
When the plate roll 32 is made to rotate at a constant speed in the drawing, the speed of the film 31 passing the expander roll 36 changes. When the plate bobbin 32 is in a position shown in FIG. 24, the speed of the film 31 passing the expander roll 36 becomes zero.
The forced dancer roll 35 performs a function of keeping constant the speed of the film 31 in front of the pass roll 33. The forced dancer roll 35 is forced to move in the direction of an arrow mark by a cam (not shown) so that the speed change of the film 31 caused at the expander roll 36 by the plate bobbin 32 does not affect the front of the pass roll 33. An error portion, wherein the speed change is not completely negated by the forced dancer roll 35, is negated by a free dancer roll 34, moved in the arrow mark direction.
The function of the expander roll 36 is shown in FIG. 25. The expander roll 36 is a roll curved in a direction as shown in FIG. 25, and the curved direction is adapted to be maintained the same if the expander roll 36 is rotated. The film 31 becomes larger in width at a point where it is separated from the expander roll 36 than its width at a point where it is in contact against the expander roll 36. Thus, the film 31 is expanded in the width direction, as indicated by the arrow marks 37. If wrinkles 38 are caused in, for example, the film 31, the wrinkles are removed after they have passed the expander roll 36 under proper conditions. The film is thus wound in a wrinkle-free condition around the plate bobbin 32.
A pass roll of a straight shape, instead of the expander roll 36, can be used. When the film 31 is thin, better winding conditions can be obtained with the expander roll 36.
The conventional plate winding method has the following problems.
When the plate bobbin 32 is rotated to the position of FIG. 24, the film 31 comes into contact at the same time against the whole face of the plate bobbin 32. When the film 31 is of a material through which it is hard to pass air, like an organic film, air is "swallowed up," or trapped, between the film 31 and the plate bobbin 32. As a result, after the film has been wound many times, the film 31a wound by the plate bobbin 32 is swollen, as shown in FIG. 26, thus resulting in an inferior winding operation. The trapping of the air is less when the winding speed is slow, and is more abrupt when the speed becomes fast.
When the winding operation of the film stops, the expander roll 36 stops for each half the rotation of the plate bobbin 32 so that a tension variation is caused in the film 31 by the inertia of the expander roll 36 when switching from stop to rotation. When the tension variation is normally 10% or more, wrinkles are likely to be caused in the film 31.
The winding speed of the plate bobbin 32 cannot be made larger because of the two reasons described above.